ES 10
Extra Credit Problem - Dante's Peak
Answer Sheet

This answer sheet is designed to give a very brief set of answers to the
questions in the
Dante's Peak
extra credit problem. There are a
number of very good, detailed web sites which have answers to common
questions about Dante's Peak, and I will not bother trying to
reproduce what others have already done better than I ever could.

Instead, I will briefly give some answers, and then pointers as to where
to go if you want to know more.

Part A: Important social and political factors

This question could easily be the subject of a very long research paper,
but for this assignment, brief was great. There are lots of social,
economic, and political factors which need to be taken into account in
a potential eruption situation.

First off, nobody wants to see people killed if it can be avoided. So people's
safety has to take absolute priority. That said, how do you balance protecting
them physically and ruining them economically? If you predict an eruption,
and you alert people, and the towns are evacuated, and the volcano erupts,
you're a hero -- as happened to David Harlow and
Jack Lockwood
(two of the technical consultants to the film)
at the 1991
Mt. Pinatubo eruption in
the Philippines. But how unequivocally can you predict that eruption? If you
predict it, and the town freaks, and nothing happens, you will destroy your
reputation, potentially the town's reputation, certainly your agency's
reputation, and you may end up killing people in an unnecessary panic.

You can see the problem, probably. You need to alert people when there is
reason to alert them. You need to give people the best information you can,
and make sure they understand it -- simply dumping it on them is unlikely
to be a good thing, since most people just don't know how to interpret the
potentially equivocal data. You need to take into account the potential harm
to a town's economy and to the people's lives. And you sometimes need to do
all this in an incredibly pressure-packed environment.

Doing all this takes fortitude, sensitivity, good judgement, and not a small
amount of luck.

We had originally wanted to show the
NOVA
program on the Pinatubo eruption,
but we were unable to get a copy quickly enough to show in class. It would
have proven interesting for this assignment, because you could easily compare
real life to the movies...oh well. But watch it if you ever have the chance.
It is a fascinating story.

Incidentally, a couple people expressed surprise when they learned that
Mammoth Lakes is in a volcanic region. It is indeed. Mammoth Mountain
itself is a large ``plug dome'' built up of very viscous rhyodacitic lava
(a composition between rhyolite, the lava with the highest silica content,
and dacite, the next highest) from a series of eruptions between 50,000 and
220,000 years ago. It sits at the southern end of a belt of
volcanic cones and lava flows which runs all the way up to Mono Lake east
of Yosemite. But that's not the most important part: the Mammoth Lakes area
sits inside a humungous volcanic caldera (a caldera is a crater more than
1 km in diameter), which is about 17 by 32 km in size and was formed in a
huge eruption about 760,000 years ago. This is called the Long Valley Caldera.
The most recent eruption near Mammoth Lakes was about 250 years ago, and even
today there are still hot springs and other such activity.

In May 1980, there was a massive swarm of earthquakes, including four magnitude
six earthquakes in less than 72 hours, near the southern edge of the Long
Valley Caldera. This, coupled with information that an area in the center of
the Caldera (called the ``resurgent dome'') was rising, got a lot of
seismologists, volcanologists, and geologists worried. There was in fact
an alert put out saying that an eruption was a distinct possibility. None
happened, but unfortunately, the (distorted) word got out that Mammoth Lakes
was going to be destroyed. Property values plummeted, and lots of economic
trouble ensued for the town. Of course, the eruption didn't happen. Many of
the people in the town harbor a lot of resentment toward the USGS as a result
of the lost business and the stress they've been put through. Here are a
couple of recent news stories from the local Mammoth paper, talking about the
situation with the town and its reputation, published on
8 September 1996 and
16 February 1997, respectively.

The problem is that the area is still in a state of unrest, and eruptions will
happen -- but volcanology is not yet in a state of being able to say when.
Anyway, the point is that the 1980 thing mentioned in Dante's Peak really
did happen -- one of the points of realism in the movie.

Part B: Did Dante's Peak do a good job of discussing these?

While I thought they really oversimplified these issues, if you gave me a
reasoned answer either way, you got the full 10 points.

Part C: Volcanic and volcano-related phenomena in Dante's Peak

Dante's Peak showed lots and lots of different volcanic and related
phenomena. I asked you to name five. Here's my (probably incomplete)
list of the phenomena that I noticed, in no particular order:

earthquakes

phreatic eruptions

ashfall

lava flows

landslides

hot springs

carbon dioxide (CO2) and
sulfur dioxide (SO2) emissions

highly acid water in the lake

lahars

pyroclastic flows

lightning in the ash column

harmonic tremor

volcanic bombs

lava dome

I will only touch on the highlights. While earthquakes are a common
accompaniment to volcanic eruptions, the size of the earthquake depicted in
Dante's Peak during the first (phreatic) eruption is ridiculously large.
Buildings don't collapse like the ones in the movie did without a magnitude
7 or so earthquake, but magnitude 7 earthquakes are (to my knowledge) unheard
of during volcanic eruptions. The houses collapsing -- that's just Hollywood.

The lava flows really annoyed me. The lava shown in the movie (especially in
the scene where they are in Grandma's cabin) is much, much too fluid to be
erupted at
Cascade
volcanoes (with one very specific exception --
Newberry Caldera
south of Bend, Oregon). The Cascade volcanoes are generated
by subduction of the Juan de Fuca Plate under Washington, Oregon, and northern
California, and have much more rhyolite, dacite, and andesite than they do
basalt lava flows, like in the movie. It really annoyed me to have Hollywood
jazz this up in such a dumb fashion - like the pyroclastic flow sequence was
not good enough?

Incidentally, the scenes with Harry and his cohorts flying around in the
helicopter around the lava dome were all filmed at
Mt. St. Helens. Lava
domes are typical in Cascade volcanoes, because the types of lava
erupted in most Cascade volcanoes is pretty thick, gooey stuff, and tends
to make domes pretty easily.

And here's what the
USGS
has to say about Harry's (Pierce Brosnan) attempt to drive across a lava flow:

A: No. Any attempt to drive across an active lava flow, even one that has
partly solidified to form a thin crust, is likely to lead to disaster. With
a temperature of 1,700 degrees Fahrenheit or higher, fresh lava will quickly
melt rubber tires and ignite gas tanks. And if a vehicle gets stuck in
moving lava, well, you know the rest of the story.

In other words, don't try this at home, kids.

Hot springs are common in volcanic areas, such as Mammoth Lakes, but while
they can undergo changes in an eruption, they don't heat up like in the
movie. You wouldn't get parboiled in seconds - you'd have plenty of time
to notice it was hotter than usual and get the heck out. But of course the
couple in the movie were having a quick tryst, and all disaster/horror
movies are required to have the ``couple who messes around'' killed in
some horrible way, so...

Carbon dioxide can actually kill trees and wildlife near volcanoes, even
when they aren't in an active eruption. There are large areas in the Mammoth
Lakes basin (south of Mammoth Mountain) where trees have died off due to
high carbon dioxide levels in the ground. This is particularly prevalent
near
Horseshoe Lake.

While lakes in volcanic craters can be highly acidic, they don't eat aluminum
boats or engines. And they don't change acidity anywhere near as quickly as
in the movie. Plus the lake in the movie isn't even a crater lake. And the
lake is acid enough to eat the boat and the boat's engine, but not to eat the
flesh off the dead fish? All of this adds up to a big fat
``yeah, right, I don't think so.''

Now, this is not to say they didn't get somethings very right. I thought that
the depictions of ashfall, landslides, lahars (which of course offs the boss
who doubted Harry), and the pyroclastic flow at the end were pretty good,
myself. Well, if you ignore the fact that pyroclastic flows move one whole
hell of a lot faster than any Forest Service truck, anyway.

There certainly have been ashfalls similar to those shown when the dumbo wonder
kids are driving up to Grandmas; for example, Yakima, WA was pretty well buried
by ash after Mt. St. Helens blew. Lightning is a pretty common occurrence in
volcanic eruptions, largely due to static electricity building up in the ash
column. There is a really nice picture of volcanic lightning on the cover of
the 28 February 1997 issue of Science; for those of you who don't have
access to Science, there's another nice one below.

Figure 1.
Volcanic lightning generated during the 18 May 1991 eruption of Sakurajima
Volcano in Japan.

Image by SVO.

Landslides along the sides of
volcanoes are common occurrences. Lahars can be extremely dangerous and
destructive, and are easily capable of taking out bridges as shown in the
movie. Some lahars from Mt. Rainier have reached as far as Puget Sound,
moving through what is now an area populated by close to 350,000 people. These
mudflows are considered a major hazard at Mt. Rainier.

Pyroclastic flows are incredibly destructive and certainly capable of
doing the sorts of damage they show in the movie. The lateral blast from
Mt. St. Helens in the climactic 1980 eruption completely destroyed the
forest north of the mountain for a range of up to 18 miles. These flows are
highly dangerous -- if you're ever in an area where a pyroclastic flow is
potentially going to happen shortly, get the hell out of there!

Overall, the movie was a balance of good stuff and some really awful stuff
as far as the phenomena described in it.

Part D: What kind of lava is shown in the movie?

The lava in the movie is pahoehoe lava, very fluid and basaltic (remember
that basaltic lavas are pretty unusual in Cascade eruptions). You can tell
this especially clearly when it breaks down the wall in Grandma's cabin.
However, I can see where you might have been confused when they tried to drive
over the flow. In that scene, the lava looked pretty rough and blocky, and
you could easily have mistaken it for a'a.

Because of this confusion, I just gave everyone 5 points for that question.

Part E: What is a phreatic eruption?

Part F: What is a pyroclastic flow?

One sidelight, though. Pyroclastic flows can travel upwards of 200 km/hr.
You can't outrun 'em and you can't outdrive 'em at those speeds. The movie
got it wrong.

Part G: How many dead squirrels did the kids find, and did the dog live?

The kids found two dead squirrels on the trail to the hot springs, though
Grandma said that dead ones were popping up all over the place. And yes,
the damn dog lives.

Just for once, couldn't we have the damn dog die? I mean, the dog
lives in every bloody disaster flick I've ever seen (and I've seen a lot of
them). The damn dog even lives through the destruction of LA in
Independence Day! (OK, so at least the aliens did us all a favor and
got rid of LA, but still, couldn't they have also killed the damn dog?)

Where to go for more information

There are lots of good references for Dante's Peak-related stuff. Here's a few
of the more interesting ones, but it's a very incomplete list: